Process for the manufacture of pig iron



Nev. 23, 1937.

M. PASCHKE El AL 2,100,086 PROCESS FOR THE MANUFACTURE OF PIG IRON Filed March 28, .1935

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PIG

Max

IRON

Paschke, Clausthal-Zellerfeld, and Eugen Pcetz, Duisburg-Huttenheim,

Germany, as-

signors to H. A. Brassert & 00., Chicago,

1 Application L In 4 Claims.

This invention relates to processes for the production of pig iron.

In the state of the art as it exists at the present day iron ores can only'be smelted effectively if 5 too much limestone is not required for binding the sulphur present in the ore and in the fuel. The necessary quantity of limestone increases as the proportion of acid, particularly silicic acid, contained in the ore increases and also as the 0'sulphur content increases. When the content of these constituents exceeds a. certain proportion, .which depends. on the market conditions, the ores can no longer be worked up economically by the ordinary reduction process owing to the low yield of iron and the high consumption of fuel. This is a very great disadvantage, since there are very many such ores which are still useless and valueless at the present time. Attempts have been made to free the ores from their content of silicon by various dressing processes, for example by magnetic separation, but these attempts have generally been'uiisuccessful on grounds of economy and in those cases in which the various minerals had intimately coalesced the attempts were also unsuccessful on technological grounds. On the other hand, an efiicient.

means, namely calcining or si'ntering, has been found for the desulphuri'zation of the ores.

By the smelting processes hitherto usual a useful pig iron having a low content of sulphur is obtained. It has also been proposed 'to effect only a rough desulphurization, for example to about 0.1-0.2% 8,, inthe blastfurnace with the usual basic slag and to refine the pig iron after being tapped from the furnace by,promoting the separation ofmanganese sulphide or in the electric furnace with a limey slag. It has further been proposed, inorder to regularize the operation and to'economize coke, to allow the pig iron and basic slag to flow from the blast furnace continuously into fore-hearths and to allow-themto react upon one another there. After-this the pig iron was then in some cases to be converted directly into steel by refining it with an air blast.

Now the present invention provides a process which enables ores which are rich in acid, particularly silicic acid, or in sulphur to be successfully smelted with a fuel containing a greater or smaller proportionof suphur. The new process is based on the novel idea, which upsets all previous conceptions regarding the art of iron production, of entirely'dispensing with desulphurization in the blast furnace and'removing the sulphur from the iron only after it has been tapped off from the blast furnace in any suitable man- March 28, 1935, Serial No. 13,508 Germany March 29, 1934 of the type of a charcoal blast furnace slag. By 5 i this means the yield of iron is considerably increased and the fuel consumption is reduced.

The drawing represents a curve showinghow the free-running temperatures of ablast furnace slag containing 12-15%a1umina vary with the 10 content of silicic acid. The temperature minimum is at a content of 44% SiOz (CaO:SiO2=1). 0n the basic side the temperatures rise steeply, on the acid side gradually. In the usual coke blast furnace slags the ratio CaO:Si0z is always 15 greater than 1 and is on the average about 15, corresponding to a content of 34% silicic acid. The corresponding free-running temperature is 200 higher than with a content of 44% S102 and approximately 100 higher than with a content of SiOz. I In the acid process, therefore, (as in the charcoal blast furnace) the temperature of the hearth can be kept considerably lower than in the usual basic process.

In'the process accordingto the invention the sulphur is taken up for the most part by the pig iron, since acid slags do not effect any or only 'a slight desulphurization. On the other hand, y it probably escapes in the form of gas in larger quantities than is otherwise the case. Because 30 sulphur reduces the capacity of iron for absorbing carbon, a pig iron is formed having a lowcontent of carbon and a high content of sulphur, for example 2.9% carbon and 1.2% sulphur, which would be either white. or mottled on solidification according to the content of silicon.

I This iron is desulphuriz'ed in known manner as soon as possible after it has been tapped and while it is still'fluid, for example with a suitable basic slag or with manganese. The quantity of 40 basic substances required is then small. It is much greater in the blast furnace because the greater part of the basic substances is made ineffective 'by the silicic acid. As the basic substance, sodium oxide in particular can be em- 5 ployed owing to its low-melting point, and it is preferably added in the form of soda. During the desulphurization apart of the silicon, manganese and iron goes into the,slag. Therefore, correspondingly more silicic acid mustbe previ- 5o ously reduced, which gives rise to no difliculty owing to the. high silicic acid content of the mix-. ture of ore and flux. Since the alkali slag also deoxidizes and removes the gas from the pig iron, there is'formed a valuable pig iron having a 55 2 finely divided graphitic, in particular pearlitic, structure, which is particularly suitable for casting purposes. The slag obtained can be usedfor themanufacture of paving stones orglassware and the desulphurizing slag can be worked up to obtain the sulphur or sulphur compounds.-

I The process which has been'described difiers fundamentally from the usual processes by the acid character of the slag employed, which only effects little or no desulphu'rization, and by the high sulphur content of the pig iron -obtained. The known proposals for the subsequent desulphurization of the pig iron all presuppose that the greater part of the sulphur has already been removed by means of a basic slag either during or immediately after the reduction of the iron; For

carrying out the process, particularly when pig 'iron is made on a large scale, it is preferable to employ a blast furnace, but other metallurgical furnaces, for example rotary or rocking furnaces which operate either continuously or intermittently can be employed for the purpose. In the 'latter case there is the advantage that cheap dusty fuels which contain more or less sulphur, such as fine coal, small coke or coke dust, can be employed. I

. Ores other than those which are rich'in silicic acid, for example ores which are rich in titanic' acid or alumina, but above all ores which are rich in sulphur can besmelted by the process of the invention. The process also enables a coke which is richinsulphur to be employed, for example a brown coke of suflicient strength.

we c u '1. A process for the manufacture of pig iron which-comprises charging a blast furnace with iron ore and sulphur containing 'coke and adding thereto slag-producing material in quantity such thatan acid slag and a pig iron having a high sulphur content are produced, and reducing the.

: quantity of sulphur in the pig iron after tapping from the furnace, by adding desulphurizing agents to the molten iron.

.2. A process'f'or the manufacture'of pig iron- I which comprises charging a blast furnace with iron ore and sulphur containing coke and adding thereto slag-producing material in quantity such. 4 that an acid slag and a. pig iron having a high sulphur content are'produc'ed, and reducing the quantity of sulphur in the pig iron by the addition of an alkaline desulphurizing, agent to the molten iron after tapping it from the furnace.

-3. A process for the manufacture ofpig iron which comprises charging a blast furnace with iron ore and sulphur containing coke and adding 1' iron ore rich in silicic acid-and sulphur containing coke and adding thereto a slag producing substance in quantity such that an acid slag and a pig iron rich in sulphur are produced and reducing the quantity of sulphur in the pig iron after tapping from the by adding desulphurizing agentssto the molten iron.

7 MAX PA'SGHKE.

EUGEN PM. 

